1. Field of the Invention
This invention generally relates to balloon catheters and more particularly to the structure of and method of manufacture of balloon catheters.
2. Description of Related Art
Coronary balloon angioplasty involves the steps of inserting a deflated balloon into a coronary artery, advancing the balloon across a lesion until the balloon is centered at the lesion and then inflating the balloon to dilate and remove the stenosis. Significant efforts have been directed toward constructing balloons with smaller cross sections so that they can better cross a tight lesion. However, experience with these smaller balloon catheters has highlighted two desirable, but until now antithetical, characteristics. First, the balloon should exhibit very low coefficient of sliding friction to facilitate initial positioning with minimal trauma. Secondly the balloon should exhibit longitudinal or axial stability during and after inflation. This stability is needed to overcome any tendency for forces exerted by the adjacent tissue to displace or shift the balloon longitudinally in the vessel. Independent efforts have been undertaken to address the issues of sliding friction and of positional stability. However, no activities seem to have been directed toward the development of a balloon that incorporates both characteristics in a single device.
For example, Boston Scientific Corporation, the assignee of this invention, manufactures a Slider.TM. PTCA Catheter having a lubricous, bonded coating covering the exterior of the balloon. This facilitates access to a lesion and enhances the ability of the balloon to cross the lesion.
Similarly the following patents disclose other coatings adapted for use with balloon catheters:
______________________________________ 4,810,543 (1989) Gould et al. 5,026,607 (1991) Kiezulas 5,049,131 (1991) Deuss 5,102,402 (1992) Dror et al. ______________________________________
U.S. Pat. No. 4,810,543 to Gould et al. discloses articles having low friction surfaces and processes for producing such articles. Specifically the Gould et al. patent proposes treating a surface with a mixture of concentrated sulfuric acid and a low molecular weight polyhydroxy compound and removing any excess treating mixture.
U.S. Pat. No. 5,026,607 to Kiezulas discloses a method in which a protective compound, such as urethane, is coupled with a slip additive, such as siloxane and, optionally, a crosslinking agent for a protective compound such as a polyfunctional aziridine, coats the surface of medical apparatus. After setting, the material provides a lubricous surface that is tough and flexible and particularly adapted for use with balloon catheters.
U.S. Pat. No. 5,049,131 discloses a balloon catheter that can be enlarged from a first predetermined diameter to a second predetermined diameter without completely withdrawing the catheter from a body passage. In this patent it is suggested that the folds of the balloon be filled with a substance, such as a paste, that has a therapeutic or medicinal effect.
U.S. Pat. No. 5,102,420 to Dror et al. discloses a balloon catheter with an exterior coating of body effecting chemicals. In some embodiments a balloon is inflated, dusted with microcapsules containing a drug and then of deflated prior to entry into the patient. Alternately, cusps, folds and other corrugations are formed when the balloon is deflated and capture microcapsules containing the drug material. These microcapsules are then presented when the balloon is inflated.
Each of the Gould et al. and Kiezulas patents discloses methods and procedures for making a device more lubricous. However, none describes any method or procedure for improving axial stability.
The following patents describe balloons that incorporate stabilizing structures to enhance the positioning, engagement and retention of a balloon at a lesion:
______________________________________ 4,447,227 (1984) Kotsanis 4,896,669 (1990) Bhate et al. 4,921,484 (1990) Hillstead 4,927,412 (1990) Menasche 4,986,830 (1991) Owens et al. 5,002,531 (1991) Bonzel ______________________________________
U.S. Pat. No. 4,447,227 to Kotsanis discloses multipurpose medical devices. Each device has a stabilizing structure for enhancing positioning, engagement and retention of the balloon in a desired lumen. The stabilizing structure is in the form of an additional medical grade balloon or one or more vacuum responsive members, such as active or passive microsuckers.
U.S. Pat. No. 4,896,669 to Bhate et al. discloses a dilation catheter with an outer tubular balloon portion. This balloon portion has circumferential crimps at each of two end transitions and an intermediate axially extended portion with longitudinal crimps. The balloon portion expands readily to a predetermined diameter while undergoing little change in length. Stability is provided because the transition portions are capable of longitudinal extension in response to minor longitudinal contraction at the two ends of the balloon portion to reduce axial movement of the balloon portion. This characteristic is stated to reduce axial movement when the balloon is inflated.
U.S. Pat. No. 4,921,484 to Hillstead discloses a mesh balloon catheter device, analogous to an expandable stent, in which the catheter has a distal end with a tube of woven interlaced filaments forming a tubular mesh. The proximal end of the mesh can be moved toward the distal end of the mesh to expand the mesh into surrounding tissue. This particular structure is designed for location in a bladder where the mesh holds the catheter in place while allowing an obstructed fluid flow.
U.S. Pat. No. 4,927,412 to Menasche discloses a catheter adapted for use in a coronary sinus where the sinus walls are slippery, extensible and tapered in a distal direction. Prior catheters normally were subject to axial displacement while being inflated. In accordance with this patent a balloon has a truncated conical surface with outwardly facing, spaced apart, parallel concentric lands for frictionally engaging the coronary sinus. This structure is stated to provide a high retentive force for stabilizing the catheter and preventing its ejection from the coronary sinus.
U.S. Pat. No. 4,986,830 to Owens et al. discloses a valvuloplasty catheter with a balloon that remains positionally stable during inflation. Stability is achieved by providing first and second inflation ports of differing sizes so that the expanding member inflates to create a dog-bone effect that allows the balloon to surround and stabilize the expander member relative to the valve being treated.
U.S. Pat. No. 5,002,531 to Bonzel discloses an inflatable balloon with a hose-like outer skin to which is connected at axially oriented edges and an inner skin also having a hose-like shape. The outer skin acts as a holding membrane. In this particular structure, the inner skin is elastic and undergoes a considerable reduction in diameter when the balloon is deflated. This eases passage of the catheter as it is advances through or retracts from an artery.
Each of the foregoing references therefore proposes some structure for improving axial stability during inflation. Although the Bonzel patent recognizes a need for easing passage through a lesion, neither it nor any other of these references describe any method or procedure for making a balloon more lubricous. Consequently the prior art defined by these references can be characterized as providing either reduced friction when a balloon is deflated or increased friction when a balloon is expanded, but not both.
It has also been suggested that balloons be used for the purpose of carrying a stent to a vessel and for the purpose of expanding that stent. The following United States Letters Patents disclose examples of such structures:
______________________________________ 4,681,110 (1987) Wiktor 4,732,152 (1988) Wallsten et al. 4,950,227 (1990) Savin et al. 5,026,377 (1991) Burton et al. ______________________________________
U.S. Pat. No. 4,681,110 to Wiktor discloses a catheter arrangement with a main tubing that contains a radially expandable liner and a member for moving the liner out of the tubing so that the liner can expand radially outward to engage a vessel wall.
U.S. Pat. No. 4,732,152 to Wallsten et al. discloses a device and method for implanting a prothesis or stent in which the prothesis is held in a radially contracted state by the device. An expandable chamber within the device permits relative movement between the elements of the devices as to permit the prothesis to be inserted and radially expanded in the location.
U.S. Pat. No. 4,950,227 to Savin et al. discloses a stent delivery system in which a stent is positioned around the distal portion of a catheter and is sized in the retracted condition to closely surround the catheter. A sleeve extends over the margin of the stent and catheter. The catheter and stent are cooperatively constructed and arranged so that expansion of the catheter to its expanded state causes expansion of the stent including the margin of the stent from its contracted condition to its expanded condition.
U.S. Pat. No. 5,026,377 to Burton et al. discloses an instrument for the deployment or retraction of a self-expanding stent in a body canal. An elongated tubular outer sleeve includes an elongated inner core movable relative to the sleeve. The core has a grip member formed at or near its distal end that is adapted to releasably hold a self-expanding stent within the outer sleeve.
In each of the foregoing patents, a structure is provided to rigidly position a device corresponding to a contracted stent on the distal end of the catheter in a fixed position so that the stent or similar device does not move relative to the end of the catheter as the distal end passes through the body to a final site. These structures complicate stent delivery systems and their use.